In search of butterfly origins.

To determine the sister taxon to butterflies, the relationships among the macrolepidopteran superfamilies were investigated using sequence data from the ND1 gene of mitochondrial DNA. Both sequence data and translated amino acids were used. We examined how different models of amino acid evolution (nonadditive) affected the inference of tree topology. We then added previously published sequence data from the 18S and 28S subunits of ribosomal RNA. In most analyses, regardless of data type and treatment, the Hedyloidea is either the sister taxon to butterflies or derived within the butterfly clade. These molecular results are compared to a reanalysis of morphological characteristics. The reanalysis of morphology agrees with Minet's 1991 hypothesis of hedyloid relationships. Analysis of combined molecular and morphology data supports the hypothesis that hedylids are the sister group to butterflies. Scott's hypothesis that hawk moths (Sphingidae) are the sister taxon to butterflies is discounted.

Systematics of holometabolous insect orders based on 18S ribosomal RNA.

Phylogenetic relationships of 19 species representing nine holometabolous insect orders and three outgroup orders were examined using sequence data from two-thirds of the 18S nuclear ribosomal RNA molecule. Of 1330 aligned nucleotide sites in 19 taxa, 460 were variable and used for phylogenetic analysis. Parsimony analyses resolved relationships in a few groups but left the most controversial questions regarding relationships among major lineages unresolved. All analyses supported a clade with Lepidoptera and Trichoptera as sister taxa most closely related to Diptera. Mecoptera and Siphonaptera were most often linked basally to this group, supporting the existence of the Mecopterida superorder. Phylogenetic affinities of this superorder and remaining lineages, Coleoptera, Hymenoptera, and neuropterids, were ambiguous. In contrast, distance analysis produced a tree supporting one of three morphologically based hypotheses. Neuroptera and Hymenoptera were placed as sister taxa ancestral to Mecopterida, with Coleoptera basal to all orders. The inability of the 18S molecule to resolve ancient divergence events may be due to the rapid divergence of holometabolous orders, resulting in few synapomorphies.

Phylogenetic studies of ribosomal RNA variation in higher moths and butterflies (Lepidoptera: Ditrysia).

The selection of exemplars has been shown both theoretically and empirically to affect tree topology, but the importance of the number and nature of taxa used to represent higher taxonomic lineages in molecular studies is rarely stressed. In our rRNA study of higher moths and butterflies (Lepidoptera: Ditrysia), the selection of different exemplars and outgroups caused major tree rearrangements. We also examined the effectiveness with which conserved rRNA regions track the diversification of Lepidoptera. Homoplasy is as prevalent at the few variable sites of conserved regions (18E, 18J, 28F) as at the many variable sites of a more rapidly evolving region (28B). Finally, 28B sequence variation differs qualitatively among lepidopteran superfamilies of presumed comparable age, the Papilionoidea (true butterflies) and Noctuoidea (cutworm moths and relatives).

Sequence evolution in mitochondrial ribosomal and ND-1 genes in lepidoptera: implications for phylogenetic analyses.

A 2,256-bp sequence of the mitochondrial genome of a lepidopteran (Spodoptera frugiperda) contains tRNAs for valine and leucine, the 16S rRNA, and three-quarters of the ND-1 presumptive protein-coding gene. A 64-bp stretch of unknown function was located between the rRNA and leucine tRNA. Sequence divergence in the 16S rRNA obtained from alignment with published insect sequences is consistent with phylogenetic hypotheses, in that Diptera and Lepidoptera are more closely related to each other (24% sequence divergence) than either is to Hymenoptera (31%). Within the ND-1 gene, sequences for four additional Lepidoptera were generated for a 314-bp region and contrasted with published sequences for the locust and Drosophila. Sequence divergence in this region was consistent with accepted phylogenetic relationships, but results of parsimony analyses were not. Cladograms consistently recovered accepted higher level relationships (monophyly of Lepidoptera), despite high homoplasy, but were unable to resolve superfamily and family relationships within Lepidoptera, regardless of the outgroup or character subset analyzed. Character analysis indicated that homoplasy was decreased at higher levels when first- and second-codon sites were used exclusively. At the lowest level (families), resolution was enhanced by inclusion of third-codon sites. Inability of molecular data to recover a well-established phylogeny may be rectified by additional characters or taxa, but it is clear that homoplasy is sufficiently high to caution against the acceptance of relationships generated with this molecular region that are not extremely robust.

DNA restriction polymorphism in wild isolates of Spodoptera frugiperda nuclear polyhedrosis virus.

Restriction endonuclease analysis was used to examine variation in DNA of 22 wild isolates of Spodoptera frugiperda nuclear polyhedrosis virus (SfNPV). Eleven of the 15 isolated from Louisiana were distinguishable based on restriction fragment profiles from the enzymes BamHI, HindIII, and EcoRI. There was significant genetic variation in SfNPV isolates within single agricultural fields. Nucleotide sequence divergence values, based on restriction fragment profiles, indicated that genetic variation among isolates foreign to Louisiana (Ohio, Ecuador, Mexico, Georgia, Colombia, and Venezuela) was greater than that among the Louisiana isolates. However, certain foreign isolates were similar to or identical with Louisiana isolates. Genetic variation of the viral DNA was not influenced by the insect's host plan species.

Estimating the degree of sperm precedence in laboratory mating experiments: a maximum likelihood method.

Allozyme polymorphisms have been used frequently in laboratory mating experiments to study patterns of sperm utilization in multiply mated females. In some instances, due either to chance or to design, there is a diagnostic difference between male genotypes that allows unambiguous assignment of paternity. In other instances, there is some overlap in allelic composition of males, so that attribution of paternity is often uncertain. This paper presents a statistical method for analyzing data of the second sort obtained from twice-mated females, based on the principle of maximum likelihood. The method allows the estimation of a mating parameter, psi the frequency with which sperm from the first male fertilizes the female's eggs. Various hypotheses about the null value of psi may be tested by a likelihood ratio test statistic. Also presented is a method of testing for homogeneity in psi values across different broods produced by the same female.

Linkage relationships of eleven enzyme loci in the Aedes scutellaris group.

Linkage relationships of 11 enzyme loci were determined in backcrosses between Aedes polynesiensis and Aedes kesseli. Three linkage groups established were Aat2-Lap2-Me-Sex, Cat-Ao-Pgm-Idh2-Est6, and Gpi-Odh-Pgd. Lap2 and Cat have not been previously mapped in Aedes. Locus order and linkage groups were the same as those observed for seven loci mapped in Aedes aegypti. The significance of the observed similarities in chromosome organization and differences in crossover values among closely related Aedes are discussed.